Defect in Graphene May Present Bouquet of Possibilities

Flower-like defects in graphene can occur during the fabrication process. The NIST team captured images of one of the defects (figures a and c) using a scanning tunneling microscope. A simulated image from their computer models (figure b) shows excellent agreement.

Credit: Cockayne,Stroscio/NIST.

A class of decorative, flower-like defects in the nanomaterial graphene could have potentially important effects on the material's already unique electrical and mechanical properties, according to researchers at the National Institute of Standards and Technology (NIST) and Georgia Tech. In a new paper,* the team for the first time describes a family of seven defects that could occur naturally or be induced to occur in graphene, one of which already has been observed.

Graphene is renowned for its strength and conductivity, both of which are a result of its structure. For the most part, graphene is a featureless plane of carbon atoms arranged in a honeycomb lattice.

According to NIST Fellow Joseph Stroscio, defects can appear due to the movement of the carbon atoms at high temperatures when producing graphene by heating silicon carbide under ultrahigh vacuum. The easiest, i.e. requiring the least amount of energy, rearrangements graphene can make are to switch from six-member carbon rings to rings containing five or seven atoms, which keeps all the carbon atoms happy with no unsatisfied bonds. The NIST researchers have discovered that stringing five and seven member rings together in closed loops creates a new type of defect or grain boundary loop in the honeycomb lattice.

According to NIST researcher Eric Cockayne, the fabrication process plays a big role in creating these defects.

"As the graphene forms under high heat, sections of the lattice can come loose and rotate," Cockayne says. "As the graphene cools, these rotated sections link back up with the lattice, but in an irregular way. It's almost as if patches of the graphene were cut out with scissors, turned clockwise, and made to fit back into the same place, only it really doesn't fit, which is why we get these flowers."

The exceedingly rigid lattice already is stronger than steel, but the defects might allow it a little flexibility, making it even more resilient to tearing or fracturing.

With more experimentation, Cockayne says, researchers should be able to correlate the appearance of defects with variations in growth conditions, which should make it possible to either avoid defects entirely or produce them at will.

Moreover, while the flower defect is composed of six pairs of five- and seven-atom rings, Cockayne and the NIST team's modeling of graphene's atomic structure suggests there might be a veritable bouquet of flower-like configurations. These configurations—seven in all—would each possess their own unique mechanical and electrical properties.

A new, free software tool from the National Institute of Standards and Technology (NIST) could prove to be a breath of fresh air for architects and designers of ventilation systems for "green" commercial buildings.

With the Climate Suitability Tool,* building design teams can evaluate whether the local climate is suitable for cooling a prospective building with natural ventilation or requires a hybrid system that supplies supplemental cooling capacity. The tool is based on a model of the heat-related characteristics of a building configured to take full advantage of ambient climate conditions and natural air movement. It incorporates an algorithm—or problem-solving procedure—that crunches hourly weather data (downloaded from annual datasets for U.S. localities) and uses standardized criteria for rating the comfort of building occupants.

"We think this tool will be useful during the early stages of design, when decisions on the form of a building and its components are being made," explains NIST mechanical engineer Steven Emmerich. "It provides estimates of ventilation rates for preliminary design calculations. You can approximate how many air changes per hour will be necessary to offset heat gains due to the occupants, equipment and lighting so that comfortable conditions are maintained."

The effects of direct natural ventilation and a nighttime cooling procedure are assessed using a method devised by James Axley, Yale University professor of architecture and engineering. When the outdoor temperature is below an accepted threshold, direct ventilation through open windows and by other means can deliver the cooling to maintain the comfort zone. When the outdoor temperature exceeds the threshold during the day but drops below it after sunset, the cooler nightime air can dilute heat gained during the day and build a reserve of cooling potential for the day to come.

Results include an estimate of the total number and percentage of hours that direct ventilation would be effective over the total for the year; the percentage of hours for which ambient conditions would be too cold, hot, or humid for direct ventilation; the total number of days warranting nighttime cooling; and the estimated percentage of days for which nighttime cooling would be effective.

In a recently published article,** Emmerich, Axley, and NIST's Brian Polidoro describe the capabilities of the new sustainability analysis tool, and present results of analyses of different scenarios in four U.S. cities representing a wide range of climates: Kansas City, Los Angeles, Miami, and Phoenix. They also evaluate the impact of an adaptive thermal comfort standard for buildings, issued by the American Society for Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE). The ASHRAE standard (55-2010) includes an option for specifying a range of temperatures as opposed to setting fixed maximum outdoor temperature at which occupants will become increasingly uncomfortable.

Studies have found that occupants of naturally ventilated buildings tolerate a wider range of temperature than do people in air-conditioned structures. The researchers concluded that in cities with dry climates, such as Phoenix and Los Angeles, the adaptive thermal comfort option increases the effectiveness of natural cooling. Though not specified in the standard, humidity levels should be carefully considered when evaluating cooling and ventilation options, they recommended.

A recent study* at the National Institute of Standards and Technology (NIST) may have revealed the optimal characteristics for a new type of computer memory now under development. The work, performed in collaboration with researchers from George Mason University (GMU), aims to optimize nanowire-based charge-trapping memory devices, potentially illuminating the path to creating portable computers and cell phones that can operate for days between charging sessions.

The nascent technology is based on silicon formed into tiny wires, approximately 20 nanometers in diameter. These "nanowires" form the basis of memory that is non-volatile, holding its contents even while the power is off—just like the flash memory in USB thumb drives and many mp3 players. Such nanowire devices are being studied extensively as the possible basis for next-generation computer memory because they hold the promise to store information faster and at lower voltage.

Nanowire memory devices also hold an additional advantage over flash memory, which despite its uses is unsuitable for one of the most crucial memory banks in a computer: the local cache memory in the central processor.

"Cache memory stores the information a microprocessor is using for the task immediately at hand," says NIST physicist Curt Richter. "It has to operate very quickly, and flash memory just isn't fast enough. If we can find a fast, non-volatile form of memory to replace what chips currently use as cache memory, computing devices could gain even more freedom from power outlets—and we think we've found the best way to help silicon nanowires do the job."

While the research team is by no means the only lab group in the world working on nanowires, they took advantage of NIST's talents at measurement to determine the best way to design charge-trapping memory devices based on nanowires, which must be surrounded by thin layers of material called dielectrics that store electrical charge. By using a combination of software modeling and electrical device characterization, the NIST and GMU team explored a wide range of structures for the dielectrics. Based on the understanding they gained, Richter says, an optimal device can be designed.

"These findings create a platform for experimenters around the world to further investigate the nanowire-based approach to high-performance non-volatile memory," says Qiliang Li, assistant professor of Electrical and Computer Engineering at GMU. "We are optimistic that nanowire-based memory is now closer to real application."

Care for a Spot of (Green) Tea? New NIST Reference Materials for Popular Diet Supplement

The National Institute of Standards and Technology (NIST) has released a suite of green tea reference materials to help manufacturers evaluate the composition of their products and assure researchers of the accuracy of analytical methods for studying the human health effects of this popular beverage and dietary supplement. The new standard reference materials (SRMs) were prepared as part of an ongoing collaboration with the National Institutes of Health Office of Dietary Supplements.

Green tea has been long prized not only for its taste but also for purported health benefits and medicinal value. Use of these green tea reference materials will improve the measurement precision and accuracy of measurements of constituents in green tea products available as dietary supplements.

Credit: Baum/NIST

People have cultivated and consumed tea for at least the past 3,000 years and perhaps much longer than that. The origin of the use of Camellia sinensis (green tea), indigenous to Southeast Asia, is the subject of competing legends. Although there are various versions of the story, Chinese legend records that Emperor Shen Nong discovered the rejuvenating effects of tea when a few leaves fell into his pot of boiling water nearly 5,000 years ago.

Green tea, which is made from the leaves of the plant that are dried without allowing them to oxidize, has been long prized not only for its taste, but also for purported health benefits and medicinal value. Beginning with Shen Nong, proponents have claimed that green tea improves digestion and heart health.

Green tea is rich in antioxidants, notably the phytochemical class "catechins," which some researchers believe account for its potential health benefits. This has spurred interest in studying the chemistry of green tea and its extracts and in evaluating amounts of these antioxidant substances during and after the manufacture of green tea dietary supplements.

The NIST green tea SRMs are natural matrices, meaning they are derived directly from the plant. Unlike purified chemicals, reference materials of this type allow researchers to measure a well-known sample with all the chemical complexity of the natural product. Using as many as five methods of analysis, NIST and collaborating laboratories have determined concentrations of seven catechins and gallic acid, three xanthine alkaloids (including caffeine), theanine, and toxic elements (arsenic, cadmium, lead and mercury) in SRMs 3254 Camellia sinensis (Green Tea) Leaves, 3255 Camellia sinensis (Green Tea) Extract, and SRM 3256 Green Tea-Containing Solid Oral Dosage Form.

These SRMs are the first green tea-containing reference materials with certified values for catechins. It is anticipated that use of the reference materials will improve the measurement precision and accuracy of measurements of constituents in green tea products available as dietary supplements.

SRMs are among the most widely distributed and used NIST products. The agency prepares, analyzes and distributes more than 1,200 different carefully characterized materials that are used throughout the world to check the accuracy of instruments and test procedures used in manufacturing, clinical chemistry, environmental monitoring, electronics, criminal forensics and dozens of other fields. For more information, see NIST's SRM website at www.nist.gov/srm/.

The National Institute of Standards and Technology (NIST) is holding a special industry workshop on June 2 and 3, 2011, at the NIST laboratories in Gaithersburg, Md., to assess interest in forming a new government-industry consortium dedicated to developing neutron-based measurement tools for "soft materials" tailored to manufacturers. The work potentially could aid a broad range of industries from plastics to pharmaceuticals.

Soft materials—so named in contrast to more ancient materials like metals and ceramics—are generally formed of large, organic molecules. The range of soft materials in modern manufacturing is huge. Plastics are soft materials, but so too are the synthetic membranes used in water filtration and fuel cells; protein-based pharmaceuticals, food additives and preservation agents; engineered tissues for advanced medical therapies; advanced lubricants; and even glasses.

Generally amorphous and with complex chemical and physical properties, soft materials present unique measurement challenges. Beams of low-energy neutrons ("cold" neutrons) at the NIST Center for Neutron Research (NCNR) are ideal for probing the behavior of many soft materials, according to NIST polymer scientist Ronald Jones, because neutrons are good at imaging the low-density, relatively large molecules typical of soft materials.

"Neutrons have been used for a long time by people in academia to look at the shape, size and properties of large molecules at the nanoscale," says Jones, "but much of industry looks at this as a very powerful, but inaccessible technique. One of the things we're trying for with this consortium is to make it more accessible. We want to help develop the techniques specifically needed for manufacturing processes."

Neutron probes can help answer questions ranging from how a particular polymer flows into molds during manufacturing to how biopharmaceutical proteins react with the surfactants meant to keep them from clumping together or sticking to surfaces, says Jones. "We can watch these things, as they happen, at the nanoscale."

The two-day "NIST Workshop on Neutron Measurements to Advance the Manufacture of Soft Materials" will combine discussions of research opportunities in soft materials that could best be addessed by neutron techniques with presentations on the capabilities of the NCNR neutron beam lines. The meeting also will discuss NIST's planned "nSoft" consortium to develop advanced neutron-based probes for soft materials. The consortium would be administered by NIST. Consortium research and development would be conducted by NIST staff members along with at least one technical representative from each participating member company.

NIST Seeks Comments on Draft Guide to Cloud Computing

The cloud computing research team at the National Institute of Standards and Technology (NIST) is requesting public comments on a draft of its most complete guide to cloud computing to date.

NIST Cloud Computing Synopsis and Recommendations(Special Publication 800-146) explains cloud computing technology in plain terms and provides practical information for information technology decision makers interested in moving into the cloud. Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources—for example networks, servers, storage, applications and services—that can be rapidly provisioned and released with minimal management effort or service provider interaction.

The Federal CIO has asked NIST to lead federal efforts on standards for data portability, cloud interoperability and security. The goal is to help the federal government reap the benefits of cloud computing.

"Cloud computing is not a single kind of system," explains project leader Lee Badger. "Since cloud computing spans a spectrum of underlying technologies and configuration possibilities, each organization's requirements call for different cloud technologies and configurations." SP 800-146 provides that level of guidance.

The new guide reviews the NIST definition of cloud computing, provides an overview of cloud environments with detailed discussions of each and then provides a section on each of the main cloud environments—Software-as-a-Service, Platform-as-a-Service and Infrastructure-as-a-Service. Each of these sections looks at the environment's scope, its capabilities, benefits, and known issues and concerns. The publication also provides information on how organizations should consider the relative opportunities and risks of cloud computing. A section on Open Issues covers computing performance, reliability, economics, compliance and data and applications security. The final section discusses general recommendations. Appendices cover typical costs of cloud computing, roles and responsibilities, acronyms, terminology and resources for further investigation.

"Moving the science and practice of evaluating EHR usability forward has required an open and transparent community effort. We hope to build on our workshop last year to catalyze collaboration among stakeholders in this important field, receive constructive feedback on methods for evaluating usability, and identify priority areas for future work," said NIST computer scientist Matt Quinn, one of the workshop's organizers.

Usability objectively assesses how easy EHR systems are to learn and operate, while maximizing efficiency. A health information technology (IT) industry task force identified usability* as one of the major factors—possibly the most important factor—hindering widespread adoption of EHRs in clinical settings. The same task force noted that usability has a strong, often direct relationship with clinical productivity, user satisfaction, lower error rate and less user fatigue.

The NIST health IT usability initiative focuses on providing guidance to the public and private sectors in the development of health IT usability standards and measures. NIST collaborates closely with industry, academia and other government agencies to share best practices on electronic health record usability as well as to gather technical feedback toward development of EHR usability evaluation methods.

NIST, AIP to Make Semiconductor Research Freely Available Online

A wealth of information on recent advances in semiconductor research is now available for free, thanks to an agreement between the National Institute of Standards and Technology (NIST) and the American Institute of Physics (AIP). The development should be welcome news to semiconductor chip manufacturers, universities and others in the computer industry who will find it less expensive to explore changes in critical measurements for semiconductor technology.

Proceedings that have been available through paid subscription or compendium volumes, such as this one from the conference's first year, are now available online at no charge.

Credit: AIP

The two institutions have made the proceedings from the International Conference on Frontiers of Characterization and Metrology for Nanoelectronics (formerly Characterization and Metrology for ULSI Technology) available for free download from both their Web sites. Until now, papers presented at the NIST-led conference series, which began in 1995, were only available through paid subscriptions.

NIST's David Seiler says the proceedings' availability should greatly help employees in the fast-paced semiconductor industry get up to speed on unfamiliar measurement and characterization issues. In addition, they can learn about new techniques and equipment being introduced to characterize semiconductors.

"These collected proceedings represent research and overviews of critical topics collected from worldwide experts in the field of semiconductor characterization and metrology," says Seiler. "As there is frequent turnover in the industry, there is constant need for training and retraining of employees. Improved access to this background will ease that process dramatically."

On the NIST Web site, the archived proceedings publications, up to and including the 2009 conference (along with slides from most of the conference invited talks), are available at www.nist.gov/pml/semiconductor/conference/archives.cfm. The AIP has made the archived proceedings publications available at http://proceedings.aip.org/semiconductor_metrology. Documents are available in searchable PDF form.

The eighth conference in the series is being held this week (May 23-26, 2011) at the MINATEC Campus in Grenoble, France. Proceedings from this week's conference will be available online in the near future. Information about AIP is available at www.aip.org/aip.

Broadening Uses Put MEMS Technology on the Map(s)

Behind the smart phone's continuing transformation into the quintessential multipurpose tool is the rise and diversification of microelectromechanical systems (MEMS), tiny machines that work the speakers, projectors, gyroscopes and other built-in gadgets that are inspiring a profusion of mobile applications.

To date, the MEMS industry has earned the bulk of its global revenue—about $7 billion in 2010—from sales of accelerometers (for airbags) and other sensors for the automotive industry along with components for ink-jet printers, displays and hard-disk drives. But it's a sign of their rise in status that MEMS are getting singled out for recognition by both the semiconductor and electronics industries in their respective technology roadmaps. Industry roadmaps are forecasts of technology advances and processing improvements necessary to sustain progress in enhancing the performance of products while minimizing manufacturing costs.

"Until only recently, MEMS devices have been viewed as distant cousins to computer chip technologies and consumer electronics," says Michael Gaitan, leader of the Enabling Devices Group at the National Institute of Standards and Technology (NIST). "But with the rapid growth of mobile computing devices like smart phones and tablets, MEMS devices are becoming the indispensable 'eyes and ears' of information technology products."

Gaitan chaired the MEMS Technology Working Group that participated in drafting the 1,800-page technology roadmap just issued by the International Electronics Manufacturing Initiative (iNEMI). For the first time since 1994, when the consortium began producing biennnial roadmaps for the electronics industry, this year's installment contains a chapter devoted to understanding the evolution of MEMS technology and the technical challenges to achieving the manufacturing capabilities that will be required over the next 10 years.

The working group has identified key challenges and gaps in device and reliability testing, wafer-level testing, modeling and simulation tools to support MEMS design, and standardization of assembly processes and packaging.

"The MEMS industry faces a set of common technical challenges that may be solved more efficiently through cooperation," says Gaitan, who is currently working on assignment to the NIST Technology Innovation Program. "The cost of testing, for example, is rising. It now accounts for up to half of the total cost of making some MEMS devices. If this trend isn't reversed, sales and market growth will be at risk."

Gaitan now chairs a newly launched MEMS Technology Working Group that will contribute to the next version of the International Technology Roadmap for Semiconductors (ITRS). This working group is focusing on MEMS devices integrated into today's smart phones, including accelerometers, gyroscopes and microphones, as well as emerging MEMS that will enable new uses of mobile information technologies. Projecting 15 years into the future, the working group is assessing requirements for device performance, design and simulation tools, packaging and integration, and testing. Their assessment will be included in the 2011 edition of the ITRS, which will be issued later this year. The ITRS has helped the semiconductor industry continue the decades-long trend of doubling the number of transistors on a computer chip about every two years.

The MEMS Industry Group, a trade association focused on advancing MEMS across global markets, has contributed to both roadmapping activities.

NIST's participation in the iNEMI and ITRS efforts helps to guide its laboratory programs aimed at developing the measurement capabilities that industry will require to make current and next-generation technologies.

Three at NIST Win Flemming Award

Three scientists at the National Institute of Standards and Technology (NIST) have been chosen to receive the Arthur S. Flemming award, recognizing distinguished service in the federal government.

Scott Diddams, a physicist in the Physical Measurement Laboratory, Time and Frequency Division, is recognized for his path-breaking work on precision measurement using laser frequency combs. Diddams and his team have, among other accomplishments, made frequency measurements that rank as the most precise absolute measurements of any kind ever made, and developed some of the world's most precise optical frequency atomic clocks. They also have developed massively parallel, ultrafast spectroscopy for fingerprinting and measurement of chemicals millions of times faster than previously possible, and made "designer lightwaves" by synthesizing light with complete control over color, timing, intensity and other parameters, for applications from improved remote sensing to better telecommunications.

Christopher Soles, a materials scientist in the Material Measurement Laboratory, Polymers Division, is recognized for a broad range of research measuring the behavior of polymers at the nanoscale; for example, characterizing physical limits on the use of nanoimprint lithography. His work has significant implications for the semiconductor and nanomanufacturing industries. The Arthur S. Flemming Awards Commission also noted Soles' work in raising up the next generation of researchers—he has mentored two dozen postdoctoral associates, graduate students, undergraduate interns and a high school student.

Ian Spielman, a physicist in the Physical Measurement Laboratory, Atomic Physics Division, is recognized for pioneering research in quantum physics, particularly the novel use of controlled quantum systems, specifically ultracold atomic gases, to model quantum phenomena that are difficult to observe in other settings. "His successes have gained worldwide attention and represent only the beginning of a program for creating a better understanding of the natural world, which may lead to new technologies for this century analogous to those that defined the last," the commission observed. Spielman is a member of the Joint Quantum Institute, a collaboration including NIST and the University of Maryland.

The Arthur S. Flemming Awards were established in 1984 to recognize outstanding men and women in the federal government. The program is managed by The George Washington University and the Arthur S. Flemming Awards Commission, and presents a total of 12 awards annually in three categories: Applied Science, Engineering and Mathematics; Research; and Managerial or Legal Achievement. More information is available at http://flemming.gwu.edu/.